If it slows down after you wait a while, that means some other process
on the machine is using the system RAM and forcing the BDB data out of
the system cache. Find out what other program is hogging the memory,
it's obvious that BDB is not doing anything wrong on its own.

If I db_stat another large file, like dn2id.bdb, the subsequent id2entry.bdb
will be slower. So maybe it is fighting itself.

However, since I am executing separate "db_stat" processes each time, the
setcachesize would have no chance to help improve things. I will have to try
different values for slapd running.

Could be I should investigate various Solaris specific process limits as well.
It is all 64bit now, but per process limits may still be interfering.